1. Eutrophication occurs when excess nutrients, usually nitrates and phosphates from sources like fertilizers, sewage, and livestock waste, enter freshwater ecosystems. 2. This causes algal blooms that block sunlight from reaching other aquatic plants, leading the plants to die off. 3. As the algae and dead plants decompose, they deplete oxygen levels in the water, collapsing food chains and potentially killing all life in the ecosystem.

1. 5.4 Eutrophication
J. Voytilla

2. What is Eutrophication?
 It begins with the addition of excess nutrients to a
freshwater ecosystem.
 Can be a natural process BUT is usually anthropogenic.
 The “excess nutrients” are usually nitrates and
phosphates.
 PS and/or NPS Sources:
- Detergents
- Fertilizers
- Sewage
- Drainage from intensive livestock areas/farms/”factories”
- Erosion of topsoil into the water

3. How does Eutrophication work?
1. Fertilizers/pollution washes into a lake or river
2. High levels of pollutant (phosphate in particular) allow algae to
grow faster
3. Algal blooms form that block sunlight from reaching the
aquatic plants beneath them
4. Plants die
5. More algae means more food for zooplankton and other small
organisms
6. Larger fish/organisms’ populations grow
7. Algae die and are decomposed by aerobic bacteria
8. The water runs out of O2
9. Soon food chains collapse and everything dies
10. O2 levels crash even further. DOM increases and water
turbidity increases
11. Eventually all life is gone and the DOM sediments settle leaving
a crystal clear blue body of water.

4. Effects
 Rivers, ponds, and lakes covered by green algal scum
and weeds
 Foul smelling gases such as H2S are released
 Anaerobic water
 Loss of biodiversity and food chain disturbance
 Death of higher plants
 Death of aerobic organisms
 Increased turbidity of water

5. Fast vs. Slow
 Low-flow water-bodies: biodiversity is severely
reduced
 High-flow water-bodies: there is a temporary
reduction in biodiversity which can be followed by
recovery and restoration of clean water

6. Eutrophication Management Strategies
Based upon the Replace, Regulate, and Restore model that we have
looked at:

7. Eutrophication Management Strategies
Strategy Example of Action
Altering human activity Plant buffer zones between fields and
watercourses to absorb excess nutrients
Regulating and reducing pollutants at
the point of emission
Regulate the amount of fertilizer that
can be used
Clean up and restoration Dredge sediments with high nutrient
levels from the river/lake bed

8. PUT THE STAGES IN THE CORRECT ORDER.
Oxygen is used up quickly by the huge numbers of microbes as they respire.
There is an increase in the BOD and a decrease in Dissolved oxygen.
Fertilisers containing Nitrogen used by farmers are leached from the soil into lakes and rivers.
Domestic inputs such as sewage containg phospahtes empty into lakes and rivers
Fish and other aquatic animals are suffocated due to lack of oxygen in the
water.
When the fertilisers and domestic waste enter lakes and rivers, algal utilise these
extra nutrients, growing rapidly. There is an increase in primary productivity
Microbes feed on the dead plant material, resulting in them rapidly increasing in
number.
These “algal blumes” block out sunlight for plants below them causing the death
of these plants.

9. Case Study!!!
 Find a report regarding a real case of eutrophication
on the world.
 Complete the following elements:
1. Where, when
2. What were the likely chemical culprits
3. Type of feedback systems involved
4. Extent of eutrophication reached
5. Effect on the ecosystem
6. Management strategies that YOU would apply in this
case.